Vacuum interrupters are used to control the application of large amounts of electrical power to an electrical load. However, in circumstances where the voltage requirements of the load exceed the voltage rating of an individual vacuum interrupter, multiple interrupters are electrically coupled in series to form a vacuum interrupter assembly. By placing the vacuum interrupters in series, the effective voltage rating of the entire vacuum interrupter assembly is increased. To enable series operation of the vacuum interrupters, a mechanical switching mechanism is used to actuate the movable contacts of each vacuum interrupter in a synchronous or otherwise simultaneous manner. As such, when the switching mechanism is actuated it results in either the simultaneous opening or simultaneous closing of the electrical contacts of the vacuum interrupters, so as to effectuate the simultaneous switching on and off of electrical current flowing therethrough.
The simultaneous opening and closing of the contacts of series coupled vacuum interrupters is critical in order to ensure that the voltage applied is evenly distributed across each individual vacuum interrupter. If the contacts of one vacuum interrupter open before the contacts of the other, the entire terminal-to-terminal voltage is applied to only a single interrupter. As a result, the voltage rating of the vacuum interrupter whose contacts are open would be exceeded, and the vacuum interrupter would not be able to stop the current flowing through the vacuum interrupter with the open contacts. Furthermore, the sustained electrical current through the single vacuum interrupter with the open contacts would eventually result in the destruction of the vacuum interrupter altogether.
To ensure that the switching mechanism provides simultaneous switching of the contacts of each of the series coupled interrupters, most mechanical switching mechanisms employ some type of adjustment mechanism. The adjustment mechanism is configured to enable one to adjust the point at which the contacts of each series coupled interrupters opens and closes relative to each other. For example, a prior art adjustable switching mechanism, generally designated by the numeral 10, as shown in FIG. 1, is used to mechanically actuate a pair of series coupled vacuum interrupters 20 and 22 that are maintained within the housings provided by respective vacuum interrupter modules 24 and 26, which together comprise a vacuum interrupter module assembly 28. However, before setting forth the structural aspects of the adjustable switching mechanism 10, a brief description of the structural and functional interrelation of the components maintained by the interrupter modules 24 and 26 will be provided.
The series coupled vacuum interrupters 20 and 22, maintained within respective interrupter modules 24,26, include movable contacts 32A-B and respective fixed contacts 34A-B. Specifically, the fixed contact 34A of the vacuum interrupter 20 is connected to a conductive input terminal pad 40, which is configured to be coupled to any suitable power supply or electrical circuit in which electrical switching is desired. The vacuum interrupter module 24 also includes a conductive flexible shunt 50 that is used to couple the movable contact 32A to a conductive intermediate plate 60. Also coupled to the conductive intermediate plate 60 is the fixed contact 34B of the interrupter module 26. Whereas, the movable contact 32B of the interrupter module 26 is coupled by a flexible shunt 70 to a conductive output terminal pad 80, which is configured to be coupled to any suitable power supply or electrical circuit in which electrical switching is desired.
As such, when the contacts 32A-B and 34A-B are closed as shown, electrical current flows into the input terminal pad 40, through the closed contacts 34A and 32A and then through the flexible shunt 50 of the interrupter module 24. After moving through the flexible shunt 50, the electrical current passes through the conductive intermediate plate 60 before flowing through the closed contacts 34B and 32B of the module 26. After passing through the contacts 34B and 32B, the electrical current flows through the flexible shunt 70 where it exits the interrupter module 26 via the outlet terminal pad 80.
In order to simultaneously actuate the movable contacts 32A and 32B of respective vacuum interrupters 20 and 22, the adjustable switching mechanism 10 is utilized. The adjustable switching mechanism 10 provides a primary drawbar 90, which is contained within the vacuum interrupter module 26, that is coupled to a secondary drawbar 92, which is contained within the vacuum interrupter module 24, via a pair of spaced, parallely oriented, slidably movable, coupling pull rods 94A and 94B. The pull rods 94 are provided with a relatively smooth outer surface. As can be seen, the pull rods are slidably received in both vacuum interrupter modules 24 and 26, and as such, slidably pass through the adjacent ends of the modules 24 and 26 and the intermediate plate 60. Furthermore, the primary drawbar 90 is attached to the movable contact 32B of vacuum interrupter 22, while the secondary drawbar 92 is coupled to the movable contact 32A of vacuum interrupter 20. In addition, the primary drawbar 90 is coupled to a primary pull rod 100 that is actuated by a suitable electromechanical switchgear (not shown) that imparts an actuation force to the adjustable switching mechanism 10, so as to simultaneously open and close the contacts 32A-B, 34A-B. Thus, when the primary pull rod 100 is moved in the direction A, the primary drawbar 90 moves the movable contact 32B away from the fixed contact 34B. And simultaneously with the movement of the primary drawbar 90 in the direction A, the pull rods 94A and 94B move the secondary drawbar 92 in the direction A, also resulting in the movable contact 32A being moved away from fixed contact 34A. As such, electrical current flowing through the vacuum interrupters 20 and 22 is stopped. Alternatively, when the primary drawbar 90 is moved in the direction B, the movable contacts 32A-B of the vacuum interrupters 20,22 are urged toward respective fixed contacts 34A-B to enable electrical current to flow through the interrupters 20 and 22.
However, because of the variation in the relative tolerances of the positioning of the contacts 32A-B and 34A-B with respect to one another, as well as the difference in the dimensions of the coupling pull rods 94A-B and drawbars 90 and 92, the contacts 32,34 of the vacuum interrupters 20 and 22 may not open and close simultaneously. As such, the adjustable switching mechanism 10 provides a pair of pull rod adjustment assemblies 110A and 110B that are respectively associated with each coupling pull rod 94A and 94B. The pull rod adjustment assemblies 110A and 110B are maintained by the primary drawbar 90, and allow the distance between the primary and secondary drawbars 90,92 to be adjusted so that the point at which the contacts 32A-B and 34A-B of the vacuum interrupters 20 and 22 open and close can be altered so that the contacts 32,34 of the vacuum interrupters 20,22 open and close simultaneously.
Because the adjustment assemblies 110A and 110B are structurally equivalent, only the discussion of the adjustment assembly 110A will be presented, as shown in FIG. 2. The primary drawbar 90 provides a pair of horizontally oriented and spaced arms 140A and 140B which form a cavity 160 therebetween. Each of the arms 140A,140B has a corresponding vertically-oriented and axially-aligned bore 130A and 130B. It will further be appreciated that each bore 130A, 1 30B provides a gripping serration 120A, 120B that is engageable with the relatively smooth outer surface of the pull rod received in the bore. Also disposed through the arm 140A is a threaded bore 150 that is dimensioned to receive and mesh with a locking screw 152 which includes a tapered end 154. A locking wedge 162 is disposed and received within the cavity 160. The locking wedge 162 includes a beveled bore 164 that is substantially axially aligned with the threaded bore 150. The beveled bore 164 also includes a concave serrated retaining surface 166. In other words, the serrated retaining surface 166 is shaped so as to be aligned with the bores 130A and 130B, and engageable with the outer surface of the respective rod 94A received therein.
Thus, to maintain the positioning of the primary drawbar 90 relative to the secondary drawbar 92, the locking screw 152 is threaded into the corresponding threaded bore 150 of the primary drawbar 90. As the tapered end 154 of the locking screw 152 is received within the beveled bore 164 of the locking wedge 162, the serrated concave surface 166 is urged against the coupling pull rod 94A. Furthermore, because the coupling pull rod 94A is typically formed from a relatively soft material, such as fiberglass or plastic for example, the gripping serrations 120A and 120B tend to grab or otherwise bite into the pull rod 94A to hold it in place.
Therefore, as adjustment of the coupling pull rods 94 A-B are needed to maintain the necessary tolerance between the primary and the secondary drawbars 90,92 the locking screw 152 of each adjustment assembly 110A,110B is initially loosened. The loosening of the locking screw 152 results in the loosening of the locking wedge 162. Once in this state, the coupling pull rods 94A-B can be freely moved through the bores 130A-B of the primary drawbar 90. As such, the distance between the primary and secondary drawbars 90,92 can be modified so that the relative positioning of the contacts 32A-B and 34A-B can be modified so that they open and close synchronously with each other.
However, because of the relatively tight fit between the pull rods 94A-B and the bores 130A-B, a substantial amount of force is required to be applied by the user to move the coupling pull rods 94A-B therethrough, making precise adjustments difficult. Moreover, because each coupling pull rod 94A-B must be individually adjusted, a user must expend significant time and care in ensuring that when an adjustment is made that the primary and secondary drawbars 90,92 remain parallel with each other to ensure that the contacts 32A-B and 34A-B are actuated simultaneously. In addition, due to the nature of the serrated locking wedge 162 it is prone to allow the coupling pull rods 94A-B to slip over time, resulting in the gradual misalignment of the primary and secondary drawbars 90,92. Furthermore, the adjustment of the drawbars 90,92, as discussed, requires that the vacuum interrupter module assembly 28 be physically removed, or otherwise detached from the electromechanical switchgear or switching mechanism (not shown), while the associated modules 24,26 are required to be at least partially disassembled. Such an endeavor, however makes the adjustment of the switching mechanism 10 in the field tedious and time consuming, which is unwanted.
Therefore, there is a need for an adjustable switching mechanism that allows the contacts of a pair of series coupled vacuum interrupter modules to be precisely adjusted so that the contacts maintained thereby simultaneously open and close. Additionally, there is a need for an adjustable switching mechanism that provides an adjustable double-threaded part and adjustable coupling screw that allow the contacts of a pair of series coupled vacuum interrupters to be precisely adjusted without physically removing the vacuum interrupter module assembly 28 from the electromechanical switch gear or switching mechanism. Furthermore, there is a need for an adjustable switching mechanism that utilizes compression assemblies to allow the positioning between the primary and the secondary drawbars to be adjusted so that the contacts simultaneously open and close. In addition, there is a need for an adjustable switching mechanism that allows the contacts of a pair of series coupled vacuum interrupter modules to be precisely adjusted without physically removing the switching mechanism from the interrupter modules.